It is generally known that a wheel bearing apparatus with a wheel speed detecting apparatus rotationally supports a wheel of a vehicle relative to a suspension apparatus and detects the wheel speed to control an anti-lock braking system (ABS). Such a bearing apparatus generally includes a sealing apparatus arranged between inner and outer members that are rotated relative to each other via rolling elements. A magnetic encoder, with magnetic poles alternately arranged along its circumference, is integrated with the sealing apparatus. A wheel speed detecting sensor is arranged opposite to the magnetic encoder to detect the variation of magnetic poles of the magnetic encoder due to the rotation of wheel. The speed detecting sensor can be mounted on a knuckle that forms part of a suspension apparatus of a vehicle, after the wheel bearing apparatus has been mounted on the knuckle.
An example of a wheel bearing apparatus is shown in FIG. 6. The wheel bearing apparatus includes an outer member 50, an inner member 51, and a plurality of balls 52 contained between the outer 50 and inner 52 members. The inner member 51 has a wheel hub 53 and an inner ring 54 press-fit onto the wheel hub 53.
The outer member 50 outer circumference has an integrally formed body mounting flange 50b that is secured to the knuckle 65 which forms a suspension apparatus. Double row outer raceway surfaces 50a, 50a are integrally formed on the outer member inner circumference. In addition, a sensor 63 is secured on the knuckle 65 by a screw 66.
The wheel hub 53 has a wheel mounting flange 55 on its one end. A wheel (not shown) is mounted to the wheel mounting flange 55. The wheel hub outer circumference has an inner raceway surface 53a. A cylindrical portion 53b axially extends from the inner raceway surface 53a. The inner ring 54 is axially secured on the cylindrical portion 53b by a caulked portion 53c. The caulked portion is formed by plastically deforming the end of the cylindrical portion 53b. The inner ring outer circumference includes an inner raceway surface 54a. 
A seal ring 56 is inserted into the outer side end of the outer member 50. The seal ring lip slidably contacts the base 55a of the wheel mounting flange 55. An encoder 57 is fit onto the inner-side outer circumference of the inner ring 54. The encoder 57 has an annular supporting ring 58 with a substantially “L” shaped cross-section. An annular encoder body 59 is adhered to a whole side surface of the supporting ring 58. The encoder body 59 is constructed as a rotary encoder to detect the wheel speed. The encoder body 59 has N and S poles alternately arranged along its circumstances.
The inner-side opening of the outer member 50 is closed by a protecting cover 60. This cover 60 is formed from non-magnetic plate materials such as a non-magnetic stainless steel plate, aluminum alloy plate or high functional resin etc. It has a simple “flat-U” configuration. It includes a disc-shaped closing plate portion 61 and a cylindrical fitting portion 62 around the closing plate portion 61.
As shown in FIG. 7(a), the side surface of the encoder body 59, forming the encoder 57, closely opposes the protecting cover 60. A detecting portion 64 of the sensor 64 is arranged close to or in contact with the side surface of the cover 60, via the cover 60. The presence of the cover 60 prevents entry of water, iron dust, magnetized debris etc. into the space between the sensor 63 and the encoder 57. Thus, this prevents breakage of the sensor 63 and the encoder 57 as well as prevents disturbance or degradation of regular and cyclic variation of the magnetic characteristics of the encoder body 59. See Japanese Laid-open Patent Publication No. 249138/2000.
However, there are the following problems in the wheel bearing apparatus of the prior art. Since the protecting cover 60 is mounted on the outer member 50 only by a metal-to-metal fitting, sufficient sealing in the fit portion cannot be attained without providing a high accuracy of surface finish and roughness on the fitting surfaces. In addition, the cover 60 is formed with a cross-sectional configuration of a simple “C” shape. Thus, the rigidity of the protecting cover 60 is insufficient. Further, it is believed that the cover 60 would be deformed by bouncing pebbles and thus it will contact with the encoder body 59.
In order to obtain sealability for the fitting portion of the protecting cover 67, as shown in FIG. 7(b), a synthetic rubber sealing member 68 is provided on the outer circumference of a radially tapered portion 67a. The tapered portion is formed between a cylindrical fitting portion 62 and the closing plate portion 61. The sealing member 68 elastically contacts against the outer member 50. However, this is not preferable since the die-pressing at the radially tapered portion 67a, during the vulcanizing process of the sealing member 68, requires high skill and technology with respect to the accuracy of the aligning portion. The die-pressing would cause distortion in the cover 67.
In addition, the sealing member 68 is vulcanizingly adhered so that it extends to the side surface of the closing plate portion 61 as shown in FIG. 7(c). Although the generation of the distortion of the cover 67 can be prevented, the rubber of the sealing member 68 will bulge out from the bent portion to the side surface of the closing plate portion 61. Thus, it is believed that the sealing member 68 would interfere with the detecting portion 64 of the sensor 63.
Furthermore, the sealing member 68 is vulcanizingly adhered so that it further projects toward the side surface of the closing plate portion 61 as shown in FIG. 7(d). Although generation of the distortion of the cover 67 and bulging-out of the sealing member 68 from the bent portion toward the side surface of the closing plate portion 61 can be prevented, it should be necessary to arrange the sensor 63 so as to avoid interference between the projected portion of the sealing rubber and the detecting portion 64 of the sensor 63. Thus, detecting accuracy would be detracted due to an increase in the air gap between the encoder 57 and the detecting portion 64.